The present invention relates to a device for ion-particle sterilization of the inner surfaces of electrically non-conducting, pressure sensitive containers comprising a unsealed filling opening. The device comprises an evacuable chamber for taking up the containers, a gas supply line connected to the chamber, electrodes for generating a plasma located in the chamber with two electrodes allocated to each container, and an alternating current generator for charging the electrodes with an alternating voltage.
DE 44 08 301 A1 discloses a device in which the containers to be sterilized run through three vacuum chambers, of which the middle one is provided for sterilization treatment of the pressure sensitive containers by low temperature plasma. An electrode pole and a gas nozzle are inserted into each container which stands on a metallic pallet.
The sterilizing effect of a plasma is due to a mechanical as well as a chemical destruction of germs by ion bombardment. Even by applying a very low energy level, the plasma can penetrate into the smallest surface cracks and holes, whereby with increasing vacuum the temperature is reduced to such an extent that even heat sensitive containers can be treated. One disadvantage of the known device lies in the insufficient homogeneity of the plasma which comes into contact not only with the surfaces to be sterilized but also with the remaining surfaces. As a result, a sterilization time of two minutes is necessary for a sufficient sterilization quotient is reached. A sterilization time of this length is too long for industrial application.
German published patent application 21 06 736 discloses sterilizing the inner surfaces of a container with a low pressure plasma based on chlorine, bromine or iodine. In one embodiment, the containers are arranged inside a reactor which is surrounded by a coil. In another embodiment, the containers are treated in the inside of a reactor, whereby an electrode is arranged in the container and a second electrode surrounds the container. In a third embodiment, the container is also the reactor and is surrounded directly by a coil. One disadvantage is that in the first two embodiments, the containers are hit by the plasma from the outside, so that the plasma is not particularly effective in the interior of the container. In the latter embodiment, only pressure insensitive containers can be sterilized, as the vacuum occurs only on the inside of the container.
It is an object of the present invention to sterilize the inner surfaces of pressure sensitive containers with a device in which the surface to be sterilized is essentially also the plasma-limiting wall.
This object has been achieved in accordance with the present invention by arranging both electrodes outside of the respective container while closely surrounding same.
As a result of the arrangement of the electrodes according to the present invention, it is ensured, on one hand, that the same low pressure prevails inside and outside the container, while on the other hand the surface to be sterilized is also essentially the plasma-limiting wall, which results in a high degree of effectiveness of the plasma and a short sterilization time. With this capacitive excitation, the ions hit the untreated wall at a particularly high energy level, which results in a high sterilization quotient which reaches at least 10.sup.4. This sterilization quotient is defined as follows: EQU SQ=a/b
The letter a denotes the quantity of germs before sterilization, while b denotes the quantity of germs after sterilization.
When the two electrodes closely surround the container by the two electrodes in the manner according to the present invention, a small gap is created. This gap permits the vacuum there to become effective, but which, however, due to its small dimensions, prevents a plasma being activated already outside of container, that is, there where it is not required. The size of the gap is determined by the so-called Debye length, which sets the characteristic shielding length and which measures between 100 und 500 .mu.m in practical use of the present invention. Thus a great homogeneity is reached on the actual surfaces to be sterilized, so that sterilization times of only a few seconds become possible. The effective vacuum on the inside and outside of the container permits on the one hand pressure sensitive containers to be sterilized, while on the other hand, due to the high vacuum, the sterilizing temperatures are so low that even heat sensitive containers, for example, paper containers, can be treated.
In connection with the present invention, "pressure sensitive" containers here include not only compressible containers, for example those made of paper, but also containers which only sporadically break under pressure, for example, glass bottles.
The electrodes can be positioned to the container from two sides. This positioning makes it possible not only to apply the electrodes according to the present invention so that they surround the container, but also to adjust the necessary small gap in a simple manner so that the electrodes are guided practically to the point of contact on the outer wall of the container. The vacuum necessary for the outside of the container is hereby not affected.
At least one electrode can advantageously be arranged to a plurality of containers. This results in a reduction of installations per container. Thus, for example, a longer container row can be arranged between, in all, only two electrodes.
In one embodiment of the present invention, the electrodes have a recess -n the area bordering directly on the filling opening. Thus the outer area of the container directly adjoining the filling opening is also sterilized. This is particularly advantageous when the recess is also the receiver for a sealing piece arranged to the filling opening. This sealing piece can be, for example, a so-called pull-tab, which is already applied adjacent to the filling opening on the lid of the container. Container and sealing piece need not then be separately sterilized.
One particular advantage of the present invention lies therein that the evacuable volume of the chamber consists essentially only of the inside of the containers. Due to the practical arrangement of the electrodes and the wall of the container--surrounding chamber, the space of the chamber to evacuated, insofar as it is located outside of the containers can be kept very small. Although the containers are surrounded by an evacuable chamber, the practical effect is similar as when the containers themselves formed the reactor. Thus only a small amount of air needs to be pumped out.
For the purpose of the present invention, the chamber subject to an operational pressure of 1 to 100 Pa. This low pressure has a resultant low gas temperature, as is necessary for example for paper cans. The low operational pressure results further in reducing the sterilization time to a few seconds.
Non-toxic gases are chosen for the purpose of the present invention, whereby oxygen, hydrogen, nitrogen, helium, neon, argon, krypton, steam, hydrogen peroxide steam or mixtures of these gases are preferably contemplated. It has proved, however, particularly advantageous to use hydrogen or helium for ionization. These gases form the lightest and smallest possible ions in the plasma. The ions can penetrate into the smallest pores of the container and diffuse most efficiently towards -he surface at a high ionization energy level.
For the purpose of the present invention, a high frequency is provided for the alternating voltage, which frequency lies between the plasma frequencies of the ions and the electrons. Thus the permissible high frequency of 13.56 Mhz is applied.
In a particularly advantageous currently contemplated embodiment of the present invention, the chamber is configured as a so-called parallel plate reactor. Thus a great number of containers can be sterilized at the same time in a particularly cost-effective way. If, for example, twenty containers are sterilized at the same time in a sterilization time of 16 seconds, the cycle time per container is reduced in this way to under one second.